The use of flame retardants in certain electrical and electronic (E&E) plastic components is essential to ensure safety and compliance with relevant safety regulations. On average 30-50% of plastics used in E&E equipment contain halogenated flame retardants. Brominated Flame Retardants are typically preferred because it requires the lowest quantity of flame retardant for the highest fire safety. The recycling of plastics containing brominated flame retardants is technically challenging however.
The present inventors have realised that Brominated Flame Retardants contain 50-95%-wt of bromine, and can be separated into aromatic, aliphatic and cyclo-aliphatic. There are over 40 different BFR types in commercial use but only a handful of those are widely used. The aromatic Brominated Flame Retardants can be divided into three types, i.e. polybrominated diphenyl ethers (PBDEs), tetrabromo bisphenol A (TBBPA) and its derivates, and polybrominated biphenyls (PBBs). Of the cycloaliphatic Brominated Flame Retardants compounds, hexabromocyclododecane (HBCD) is the most important. Aliphatic Brominated Flame Retardants are not used in large amounts since they are less stable than aromatic Brominated Flame Retardants; they may be more effective at lower temperatures, however.
The present inventors have realised that the most widely used Brominated Flame Retardant compound nowadays is tetrabromobisphenol A, TBBPA. TBBPAs and their derivatives include TBBPA bis-(2-hydroxyethylether). Their market share is the largest one of flame retardants market world wide. TBBPA and its derivatives main use are as additive Flame Retardants for polybutylene terepthalate (PBT), polyethylene terephtalatete (PET) and ABS plastics.
The present inventors have realised that the second important type of Brominated Flame Retardants are polybrominated diphenyl ethers, PBDEs such as deca-BDE, octa-BDE and penta-BDE from which the deca-BDE is considered one of the most common compounds. Major uses for PBDEs are plastic housings of smaller office equipment and in polyolefin plastics. There has been much recent discussion concerning Bromines PBDEs toxicological effects and there have also been recent regulation changes, for example in Europe.
Decabromodiphenyl ether (DBDE) continues to be widely used as a flame retardant for plastics, particularly high impact polystyrene (HIPS). The present inventors have realised that there is a perception that these brominated flame retardants (BFR) form brominated dioxins and furans during reprocessing which are considered dangerous from an occupational health and safety perspective. For electronic plastic parts, such as those from end-of-life printers and computers, bromine extraction and relative neutralization is required to provide an economically viable solution to the brominated flame retardant problem. Yet this problem remains hereto before unsolved.
The present inventors have also realised that attitudes and regulations regarding environmental issues and recycling of plastics vary considerably around the world. While recycling in the U.S. is generally voluntary and economically driven, Europe and Asia generally have regulation governing plastics recycling. There is also a trend in Europe and Asia towards increasing the responsibility of the products producer for the end-of-life outcome of their products. Regulations are expected to drive innovation and create markets for recycled material.
The inventors have realised that the waste electrical and electronic equipment (WEEE) directive, recently set-up in Europe is pushing the need to safely and effective recycling of plastics, including those containing brominated flame retardants. This will set new requirements for the treatment of the waste products. These requirements include higher recyclability of the products material content as well as separate treatment of certain parts. Mobile phones for example contain up to 70% plastics, which are lost in the mechanical and thermal process, where only metals are collected.
The inventors have also realised that the main fractions of scrap from end-of-life electronic and electrical appliances are metals, glass and plastics. The first two of these can be relatively easily separated and reclaimed with existing technology. However, a significantly higher plastic content in future generations of appliances will dramatically alter the recycling equation, thereby forcing the sector to step up its efforts to devise improved ways of recycling WEEE.
Environmental, financial and legislative drivers are also pushing towards more rigorous approach to recycling. Currently recycling technologies are optimised for precious and ferrous metal recycling. These technologies are considered not suitable for recycling of products that are mostly of other materials such as plastics. Current technologies are also not directed at providing zero landfill. Thus there is a need to process the WEEE materials considered to be ‘waste’ in various other industries.
The inventors have further realised that there are four types of plastics which dominate the polymeric materials found in WEEE, namely acrylonitrile butadiene styrene (ABS), high-impact polystyrene (HIPS), polycarbonate (PC) and an ABS/polycarbonate (ABS/PC) blend. There are also many different polymer types of materials in WEEE, for example, with some WEEE streams some 35 types of polymer materials have been identified. Plastic sorting and separation is required to maximize economic return. Plastic enrichment and purification to a level to enable marketability is therefore required.
U.S. Pat. No. 6,335,376 describes an apparatus and method for enhancing partitioning of different polymeric materials from a mixture by density differential alteration. Float-sink baths are employed but the materials are foamed in order to affect separation.
U.S. Pat. Nos. 6,080,473 and 6,007,005 both disclose a process for manufacturing extruded ABS products includes recycling used ABS to produce a recycled ABS exhibiting predetermined characteristics and extruding the recycled ABS to produce an ABS product. The process incorporates a salt bath for float-sink separation.
A froth-flotation process for the separation and recovery of high-purity ABS from mixed plastics is disclosed in U.S. Pat. No. 5,653,867, Method for Separation of High Impact Polystyrene and Acrilonitrile Butadiene Styrene Plastics). This process uses a binary acid/salt bath to separated ABS from HIPS.
There is still a need for foreign materials (particularly metals) to be satisfactorily processed as the foreign materials downgrade the performance of recovered plastics. Plastic separation is also necessary to achieve consistent properties and upgrade performance. For example, toner cartridges by their multicomponent nature are considered challenging to recycle by reprocessing. The plastic stream recovered by direct shredding of toner cartridges contains well-adhered foreign materials, electrostatically-bound toner dust and significant levels and sizes of both ferrous and non-ferrous (principally aluminium) metals. It is therefore known to be difficult to recycle waste from WEEE because of the many different polymer types.
The inventors have also realised that materials found in WEEE are an intimate mixture of plastic, metals, foam, rubber, toner, ink, ceramics/glass, and intractables, such as additives, glue, epoxy, silicon and many other materials and elements not falling into the previous groups. Thus, one problem in the recycling of WEEE is how to deal with this complex mix of many elements. The recovery of most non-ferrous and ferrous metals and some pure streams of plastics are known. However, there still exists a difficulty in the recycling of relatively heavily contaminated and mixed streams of elements, especially those that do not readily form pure streams. To date, most of this heavily contaminated and mixed stream of elements is sent to landfill or incineration, neither of which is desirable nor sustainable. There is thus a need to provide for the recycling and/or reuse of material forming WEEE, without landfill or incineration.
The inventors have additionally realised that there are also a number of hazardous substances within WEEE which are contained within the plastic components of the WEEE, in particular brominated flame retardants (BFR) which may be a barrier to recycling. For example, housings or enclosures for computer monitors and printers are predominantly made from high-impact polystyrene (HIPS), ABS-polycarbonate blends or ABS-based flame retardant compounds, although polypropylene (PP), polycarbonate (PC) and blends of polyphenylene ether (PPE) and styrene/butadiene polymer may be used as well. In the 1990s, HIPS represented 30% of the global De-BDE consumption, and ABS accounted for around 95% of the total Oc-BDE supplied in the EU.
The present inventors have realised that mechanical recycling is a potentially effective option for large electronic parts which typically have high levels of flame retardants. However concerns over halogenated flame retardants and in particular brominated flame retardants have been ongoing. Two specific brominated flame retardants, pentabromodiphenyl oxide and octobromodiphenyloxide, are being considered for a ban in Europe.
While these plastics can be mechanical recycled and reprocessed, a major concern is the formation of brominated dioxins and furans as well as HBr, Br2 and non aliphatic compounds emissions are also hazardous.
Brominated flame retardants pose some technical problems in reprocessing (toxic fume emissions etc), melt porosity and polymer property deterioration. The production of toxic fumes during re-extrusion of brominated flame retardant plastics from waste electrical and electronic equipment is another barrier preventing the more widespread recycling of the plastics components of WEEE, such as computer housings, printers and television housings.
Still further, the inventors have realised that the reprocessing of plastics containing brominated flame retardants can lead to the formation of polybrominated diphenyl dioxins and polybrominated diphenyl furans (PBDD/F). These are highly regulated compounds and reports are that the conventional melt reprocessing of mixed plastics containing brominated flame retardants can lead to PBDD/F concentrations exceeding the regulation limits.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.
An object of the present invention is to provide an improved process of enabling the recycling of mixed plastics containing Brominated Flame Retardants.
A further object of the present invention is to alleviate at least one disadvantage associated with the prior art.